1. Field of the Invention
The present invention relates to a liquid jet head for discharging liquid from nozzles to form images and characters on a recording medium or form a thin film material, and also relates to a liquid jet apparatus using the liquid jet head.
2. Description of the Related Art
In recent years, an ink jet system liquid jet head has been used for creating characters and graphics by discharging ink droplets onto a recording sheet or the like, or forming a pattern of a functional thin film by discharging a liquid material onto a surface of an element substrate. In the ink jet system, ink or a liquid material is supplied from a liquid tank to the liquid jet head through a supply tube, and the ink is loaded into small spaces formed in the liquid jet head. In response to a drive signal, the volume of the small spaces is instantaneously reduced to discharge liquid droplets from nozzles communicating to grooves.
FIG. 12 is an exploded perspective view of an ink jet head 51 of this type. The ink jet head 51 includes a piezoelectric substrate 52 having a plurality of grooves 56 formed in a surface thereof, a cover plate 54 having a liquid supply cell 62 and slits 63 formed therein, a nozzle plate 55 provided with nozzles 64 for discharging liquid, and a flexible substrate 53 for supplying a drive signal generated by a drive circuit to the piezoelectric substrate 52. The grooves 56 have upper openings closed by the cover plate 54 to form channels. The grooves 56 are partitioned by partition walls 57, and on side surfaces of each partition wall 57, drive electrodes 59 for driving the partition wall 57 are formed. The drive electrodes 59 are connected to extension electrodes 60, which are formed on the surface of the piezoelectric substrate 52 at a rear end RE thereof. The partition walls 57 formed of a piezoelectric body are subjected to polarization processing in a perpendicular direction. By supplying the drive signal to the drive electrodes 59 formed on both the side surfaces of the partition wall 57, the partition wall 57 slips to be deformed in the thickness direction. By deforming the partition walls 57 at the time of driving under a state in which the channels formed by the grooves 56 are loaded with liquid in advance, the volume of the channels changes to discharge the ink from the nozzles 64 of the nozzle plate 55, which is bonded to a surface of the piezoelectric substrate 52 at a front end FE thereof.
FIG. 13 is a schematic top view of the piezoelectric substrate 52 and the flexible substrate 53 in a state in which the flexible substrate 53 bonded to the surface of the piezoelectric substrate 52 in the vicinity of the rear end RE is separated from the piezoelectric substrate 52 and displaced downward of the drawing sheet. The channels formed by the grooves are provided in the surface of the piezoelectric substrate 52, the channels including dummy channels D1 to Dn+1 and discharge channels C1 to Cn for discharging liquid droplets, which are arranged alternately with each other. The drive electrodes 59 for deformably driving each partition wall 57 partitioning the channels are formed on the side surfaces of the partition wall 57. The extension electrodes 60 electrically connected to the drive electrodes 59 of each channel are formed on the surface of the piezoelectric substrate 52 in the vicinity of the rear end RE. For example, drive electrodes 59c1 are formed on both side surfaces of both the partition walls 57 on the discharge channel side, the partition walls 57 constituting the discharge channel C1, and the drive electrodes 59c1 are connected to a first extension electrode 60c1. A drive electrode 59d1 is formed on a side surface of the dummy channel D1 on the discharge channel C1 side, and a drive electrode 59d2 is formed on a side surface of the dummy channel D2 on the discharge channel C1 side. Both the drive electrode 59d1 and the drive electrode 59d2 are electrically connected to a second extension electrode 60d1. The other discharge channels C2 to Cn, the dummy channels D2 to Dn+1, and the first and second extension electrodes 60c and 60d have the same structures, respectively.
On a surface of the flexible substrate 53 on the piezoelectric substrate 52 side, there are formed wiring electrodes 61 for supplying the drive signal to the drive electrodes 59. As indicated by the arrows of FIG. 13, the flexible substrate 53 is moved to the surface of the piezoelectric substrate 52 on the rear end RE side so as to be bonded to the surface of the piezoelectric substrate 52, with a wiring electrode 61d1 electrically connected to the extension electrode 60d1; a wiring electrode 61c1, the extension electrode 60c1; and a wiring electrode 61d2, an extension electrode 60d2. The same applies to the other wiring electrodes 61.
FIG. 14 is a perspective view illustrating another ink jet head (FIG. 1 of Japanese Patent Application Laid-open No. Hei 9-29977). A plurality of grooves are formed in a lower surface of a piezoelectric ceramic substrate 71 to form channels. A nozzle plate (not shown) is bonded to a surface 74 of the piezoelectric ceramic substrate 71 at a front end portion thereof, and ink cells 72 formed by the grooves communicate to nozzles of the nozzle plate. Drive electrodes are formed on each partition wall partitioning the ink cells 72 provided in the lower surface, and the respective drive electrodes are extended by extension electrodes 76 to a surface 75 via the surface 74. On the surface 74, the electrodes are insulated from one another by insulating portions 73, while on the surface 75, the extension electrodes 76 are electrically insulated from one another by insulating portions 77. The extension electrodes 76 are connected to electric wires 79 at electric connection terminals 78 provided on the upper surface of the piezoelectric ceramic substrate 71 at a rear end thereof, and thereby connected to a drive circuit (not shown). In this example, a pitch W2 of the electric connection terminals 78 is set larger than a pitch W1 of the ink cells 72, to thereby facilitate connection to an external connection circuit.
In the conventional example illustrated in FIGS. 12 and 13, a pitch P1 of the connection points between the wiring electrodes 61 formed on the flexible substrate 53 and the extension electrodes 60 needs to be set substantially equal to an arrangement pitch P of the channels formed in the piezoelectric substrate 52. In recent years, however, the arrangement pitch P2 has become smaller and smaller with the increase in number of channels. Therefore, the pitch P1 of the connection points between the wiring electrodes 61 on the flexible substrate 53 and the extension electrodes 60 also needs to have a smaller pitch, which requires strict alignment accuracy at the time of alignment and mounting. As a result, there arises such a problem that the manufacturing becomes difficult or manufacturing yields decrease.
Further, in order to form the extension electrodes 76 on the back surface side of the piezoelectric ceramic substrate 71 as illustrated in FIG. 14, the electrode pattern needs to be formed on the surface 74 of the piezoelectric ceramic substrate 71 at the front end thereof and on the upper surface 75 thereof. Therefore, there arises such a problem that the manufacturing process becomes complex and accordingly mass productivity decreases.